1. Field of the Invention
This invention pertains generally to the field of cockpit indicators or display units that provide flight information of a runway environment to the pilot or flight crew of an aircraft, and more particularly to synthetic vision systems (SVS), enhanced vision systems (EVS), or combined SVS-EVS systems.
2. Description of the Related Art
Navigation reference data and navigation data are not exact but contain inherent errors. Navigation reference data may be representative of, in part, airport surfaces and airport visual aids. Airport surfaces include, but are not limited to, locations and information delineating or defining locations of runways, taxiways, and apron areas, fixed based operators (“FBOs”), terminals, and other airport facilities. Airport visual aids include, but are not limited to, airport pavement markings, runway markings, taxiway markings, holding position markings, airport signs, mandatory instruction signs, location signs, direction signs, destination signs, information signs, and runway distance remaining signs. Navigation reference data is typically stored in a database such as, but not limited to, a taxi navigation database and/or aerodrome mapping database (“AMDB”).
A majority of existing AMDBs have been captured and maintained using geographic information systems (“GIS”). As discussed in an industry standard RICA DO-272A published by RTCA, Incorporated and entitled “User Requirements for Aerodrome Mapping Information,” GIS technology has evolved from the computer-aided design (“CAD”) industry, combining the detailed information available in engineering drawings with a geographic reference system. A GIS is a computer program that combines geographically referenced digital data with spatial and attribute analysis tools. A GIS can include many different types of data including: control networks, vector data, raster grid data, triangulated irregular networks (“TINs”), 3-D surface representations, remotely sensed data, and other digital source data such as geo-referenced drawings or airport layout plans (“ALPs”). Within a GIS, these data sources can be combined, spatially referenced, and analyzed, enabling the user to organize information and answer questions about the spatial relationships between the various dramatic layers as well as the attribute characteristics of the features. In addition to the use of GIS technology, AMDBs have also been developed by digitizing paper charts such as airport obstruction charts, utilizing CAD tools, and in text or tabular files.
DO-272A provides for aerodrome surface mapping requirements for aeronautical uses particularly on-board aircraft. One of the requirements addresses quality of the data contained in an AMDB. Quality could be associated and/or measured with parameters such as, but not limited to, accuracy, resolution, and/or integrity of data stored in any database. Because the data is not exact, the data may not coincide with the surveyed location of visible features such as the airport surfaces and airport visual aids. If this data is presented egocentrically on a display unit such as a HUD unit through which the pilot has an actual view of the scene outside of the aircraft, the visual aid may not align with the actual visible features. That is, the pilot may be presented with an angular misalignment between the actual visible feature and visual aid representative of the visible feature. Where the visual aid is depicted with a constant intensity and/or brightness, the misalignment distracts and/or annoys the pilot, thereby reducing user trust and acceptance of the display unit and the information that it provides. This lack of trust acceptance diminishes the pilot's Situational Awareness, an important safety concern in aviation.
Along with the AMDB, the lack of precision in data arises with data provided by a navigation system. Navigation systems contain inherent errors affecting the quality of the data provided by them. For example, in un-augmented global satellite navigation system, errors could be as much as 100 meters. In an augmented system such as a Satellite-Based Augmentation System (“SBAS”), the quality of data may deliver an improved signal accuracy of approximately 7 meters. In an augmented system such as a Ground-Based Augmentation System (“GBAS”), even better quality of data may deliver an improved signal accuracy of less than 1 meter. Because the data is not exact, the data provided by AMDB that is based on un-exact or inherently erroneous aircraft position data provided by a navigation system may be data not representative of the actual surveyed location of the aircraft. As discussed above, an angular misalignment between actual visible features and corresponding constant-intensity visual aids depicted egocentrically on a display unit could result, thereby affecting the pilot's Situational Awareness.